Plasma Membrane Structure and Function

copyright cmassengale The Plasma Membrane 9/7/2018 Homeostasis Balanced internal condition of cells Also called equilibrium Maintained by plasma membrane controlling what enters & leaves the cell copyright cmassengale G. Podgorski, Biol. 1010

Membrane Functions Protective barrier Communication Regulate transport in & out of cell (selectively permeable) Respond to environment Recognition Provide anchoring sites for filaments of cytoskeleton

Plasma Membrane Boundary that separates the living cell from it’s non-living surroundings. Phospholipid bilayer Amphipathic - having both: hydrophilic heads hydrophobic tails ~8 nm thick Is a dynamic structure Phospholipid

copyright cmassengale The Plasma Membrane 9/7/2018 Phospholipids Make up the cell membrane Contains 2 fatty acid chains that are nonpolar Head is polar & contains a –PO4 group & glycerol copyright cmassengale G. Podgorski, Biol. 1010

FLUID-MOSAIC MODEL FLUID- because individual phospholipids and proteins can move side-to-side within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.

Materials that are soluble in lipids can pass through the cell membrane easily

Small molecules and larger hydrophobic molecules move through easily e.g. O2, CO2, H2O Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own

Types of Transport Across Cell Membranes The Plasma Membrane 9/7/2018 Types of Transport Across Cell Membranes copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 9/7/2018 Simple Diffusion Requires NO energy Molecules move from area of HIGH to LOW concentration copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 9/7/2018 DIFFUSION Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural KINETIC ENERGY copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 9/7/2018 Diffusion of Liquids copyright cmassengale G. Podgorski, Biol. 1010

Diffusion through a Membrane The Plasma Membrane 9/7/2018 Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to LOW) copyright cmassengale G. Podgorski, Biol. 1010

Gas exchange in lungs by diffusion

Diffusion across a membrane Semipermeable membrane The Plasma Membrane 9/7/2018 Osmosis Diffusion across a membrane Diffusion of water across a membrane Moves from HIGH water potential (low solute) to LOW water potential (high solute) Semipermeable membrane copyright cmassengale G. Podgorski, Biol. 1010

Osmosis The diffusion of water across a differentially permeable membrane due to concentration differences

Diffusion of H2O Across A Membrane The Plasma Membrane 9/7/2018 Diffusion of H2O Across A Membrane High H2O potential Low solute concentration Low H2O potential High solute concentration copyright cmassengale G. Podgorski, Biol. 1010

Cell in Isotonic Solution The Plasma Membrane 9/7/2018 Cell in Isotonic Solution 10% NaCL 90% H2O ENVIRONMENT CELL NO NET MOVEMENT 10% NaCL 90% H2O What is the direction of water movement? equilibrium The cell is at _______________. copyright cmassengale G. Podgorski, Biol. 1010

Cell in Hypotonic Solution The Plasma Membrane 9/7/2018 Cell in Hypotonic Solution 10% NaCL 90% H2O CELL 20% NaCL 80% H2O What is the direction of water movement? copyright cmassengale G. Podgorski, Biol. 1010

Cell in Hypertonic Solution The Plasma Membrane 9/7/2018 Cell in Hypertonic Solution 15% NaCL 85% H2O ENVIRONMENT CELL 5% NaCL 95% H2O What is the direction of water movement? copyright cmassengale G. Podgorski, Biol. 1010

NO NET MOVEMENT OF H2O (equal amounts entering & leaving) The Plasma Membrane 9/7/2018 Isotonic Solution Hypotonic Solution Hypertonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) CYTOLYSIS PLASMOLYSIS copyright cmassengale G. Podgorski, Biol. 1010

Cytolysis & Plasmolysis The Plasma Membrane 9/7/2018 Cytolysis & Plasmolysis copyright cmassengale Cytolysis Plasmolysis G. Podgorski, Biol. 1010

What Happens to Blood Cells? copyright cmassengale

Three Forms of Transport Across the Membrane The Plasma Membrane Three Forms of Transport Across the Membrane 9/7/2018 copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 9/7/2018 Passive Transport Simple Diffusion Doesn’t require energy Moves high to low concentration Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out. copyright cmassengale G. Podgorski, Biol. 1010

Facilitated diffusion The Plasma Membrane 9/7/2018 Passive Transport Facilitated diffusion Doesn’t require energy Uses transport proteins to move high to low concentration Examples: Glucose or amino acids moving from blood into a cell. copyright cmassengale G. Podgorski, Biol. 1010

Proteins Are Critical to Membrane Function The Plasma Membrane 9/7/2018 Proteins Are Critical to Membrane Function copyright cmassengale G. Podgorski, Biol. 1010

Types of Transport Proteins The Plasma Membrane 9/7/2018 Types of Transport Proteins Channel proteins are embedded in the cell membrane & have a pore for materials to cross Carrier proteins can change shape to move material from one side of the membrane to the other copyright cmassengale G. Podgorski, Biol. 1010

Facilitated Diffusion The Plasma Membrane Facilitated Diffusion 9/7/2018 Molecules will randomly move through the pores in Channel Proteins copyright cmassengale G. Podgorski, Biol. 1010

Facilitated Diffusion The Plasma Membrane 9/7/2018 Facilitated Diffusion Some Carrier proteins do not extend through the membrane. They bond and drag molecules through the lipid bilayer and release them on the opposite side copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 9/7/2018 Carrier Proteins Other carrier proteins change shape to move materials across the cell membrane copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 9/7/2018 Active Transport Requires energy or ATP Moves materials from LOW to HIGH concentration AGAINST concentration gradient copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 9/7/2018 Active transport Example: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients. Called Na+-K+ Pump copyright cmassengale G. Podgorski, Biol. 1010

Sodium-Potassium Pump The Plasma Membrane 9/7/2018 Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential copyright cmassengale G. Podgorski, Biol. 1010

Exocytosis and Endocytosis Exocytosis---Cellular secretion Endocytosis— Phagocytosis— “Cell eating” Pinocytosis– “Cell drinking” Receptor-mediated endocytosis-specific particles, recognition.

Exocytosis- moving things out The Plasma Membrane Exocytosis- moving things out 9/7/2018 Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve cells communicate with one another. copyright cmassengale G. Podgorski, Biol. 1010

Exocytosis

Phagocytosis

Pinocytosis

Receptor-mediated Endocytosis